The 'mega-basements' built by London's super rich are being challenged in Britain's High Court

A swimming pool in one of London's luxury basement extensionsOrbital Basements
The basement extensions favoured by London's super rich will be challenged in a High Court case at the end of November, to determine how far homeowners can bypass formal planning applications, according to the Financial Times.

Building large extensions under London homes have become popular in recent years. As space in the capital is restricted, homeowners have chosen instead to dig under their existing homes, and many have annoyed neighbours in the process — they argue that the work can cause groundwater problems, and the building work is often noisy and lengthy.

The High Court case is being brought by Michael Eatherley, a Kentish Town resident who lives in a row of Victorian cottages.

He is challenging Camden council for allowing a neighbour to build a basement extension under so-called "permitted development rights," a system which allows homeowners to bypass the formal planning application process, as long as the extension is only one storey deep.

The "iceberg extensions" favoured by the very richest people such as Chelsea FC owner Roman Abramovich— which are often several storeys deep — already have to go through the formal planning process, and that means councils can reduce disruption by regulating the working hours of builders.

But local councils have a limited ability to regulate one-storey extensions, and neighbours have a limited ability to object to them. If Eatherley is successful, it will set a national precedent for homeowners having to apply formally to build a basement.

There were a total of 887 applications to build a residential basement in 2015 — that is a quarter more than in 2015, and almost double the previous peak in 2007.